A process is provided for making a split bearing assembly that has a saddle-like main body and a removable saddle-like bearing cap secured in end-to-end engagement with a body to define a journal-receiving opening.
A connecting rod and a crankcase of an internal-combustion engine has crankshaft bearings used as cast engine parts. Each of the above-mentioned bearing arrangements comprise a bearing cap formed by fracture separating. As a preparatory measure for a targeted fracture separating, each bearing arrangement in the respective bearing bore also has diametrically arranged, relatively large (macroscopic) fracture separating notches which, according to European Patent Document EP-A 0167320, are preferably produced mechanically but can also be formed by casting or forging.
For a perfect fracture separating via a clear incipient fracture in the base of the separating notch or the indentation, these fracture separating notches require a relatively small point radius (R.fwdarw.0). This explains the high tool wear that results due to fracture separating notches which are produced mechanically.
It is an object of the invention to improve a manufacturing process for a cast engine part with cast-in indentations serving as fracture separating notches such that the desired small point radius is ensured in the notch base of each indentation.
This and other objects and advantages are achieved by the manufacturing process according to the invention, by producing the indentations via separate projections provided on the core. The projections have stably constructed free projection edges. Further, in the area of the notch base of each indentation acting as the incipient crack site, each respective projection has a respective shaping radius between R=0 mm and R&lt;0.45 mm.
In an advantageous embodiment of the invention, the projections which are separate with respect to the core (customary for the shaping-out of the bearing bore) are selected from a stable material (i.e., an iron, a glass, an oxide-ceramic or a salt core). Here, with the selection of the stable material, projections are formed in a wedge shape whose free projection edges (constructed in the manner of blades) each have a radius between R=0 mm and R&lt;0.25 mm. The advantages of the projections which are separate with respect to a core is that they provide exchangeability with a resultant low material cost. A further advantage is their manufacturing/finishing results in a "sharp" projection edge.
In addition, having separate projections offers (as a further advantage) the selection of a material that has a high thermal conductivity (i.e., an iron or a ceramic material). In this case, for the increased dissipation of heat, the projections, in addition to a customary protective core coating in the area of the respective projection edge are covered with a metal oxide coating (preferably a tellurium oxide coating). As a result of this measure, in the case of an engine part formed of a cast iron material, via an increased dissipation of heat due to the tellurium oxide coating in the edge area of each base of each indentation or fracture separating notch (which acts as an incipient crack point), a chilling or a chilled zone can be generated. This chilled zone, because of its hardness, is particularly sensitive to cracks and is therefore advantageously used for forming an incipient crack in the fracture separating plane in the form of a hair crack.
In another embodiment of the invention, to promote ease of handling, wedge-shaped projections of diametrical indentations are formed as end sections of an insert which is arranged to penetrate a respective core. For reasons of cost, the projection are preferably formed of a flat-steel section. This insert is held in a securing manner in a core, such as a sand core, via form closure devices (preferably via openings).
In a further embodiment of the invention, the separate projections are connected with a ring-shaped pressure-resistant insert of a core. The insert ring is reduced in its outside diameter relative to the bearing bore of the respective engine part by an amount corresponding to a thin core sand layer to be applied in a tightly adhering manner.
Particularly, in the case of an engine part which is formed of a cast iron material and has chilled zones in the base of each indentation, this measure makes it possible to produce cracks or hair cracks directed in the fracture separating plane of the bearing arrangement. Because the shrinkage of the respective bearing arrangement in the above-mentioned chilled zones is hindered by the insertion ring in the core, the cracks or hair cracks appear as starter cracks for the fracture separating which follows.
In the case of bearing arrangements which are connected with one another by casting, such as connecting rods cast in a stack or bearing caps of crankshaft bearings of a crankcase which are integrated in a frame, the forced incipient cracks advantageously result in a reduction of tension in the connected bearing caps.
The incipient cracks produced by the so hindered shrinkage additionally facilitate the removal of the respective insert from a bearing arrangement. Here, the removal of the inserts from the indentations is ensured by the consumed coatings.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.